Switching mode power supply apparatus and power supply method thereof

ABSTRACT

A switching mode power supply apparatus includes a conversion unit to convert input power into output power having a predetermined voltage by performing a switching operation, a light emitting unit to emit light if the voltage of the output power exceeds a predetermined threshold voltage, a light receiving unit to receive the light emitted from the light emitting unit and output a signal indicative of the voltage of the output power, a switching controller to control the switching operation of the conversion unit according to the voltage of the output power indicated by the signal output from the light receiving unit, and a disconnection unit to disconnect power applied to the light receiving unit if a voltage of the power applied to the light receiving unit exceeds a predetermined trigger voltage.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation Application of U.S. application Ser.No. 12/105,519 and claims the benefit of Korean Patent Application No.2007-80035, filed on Aug. 9, 2007 in the Korean Intellectual PropertyOffice, the disclosures of which are incorporated herein by reference inits entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Aspects of the invention relate to a switching mode power supplyapparatus and a power supply method thereof, and more particularly to aswitching mode power supply apparatus that detects a voltage of powerapplied to a light receiving unit and a power supply method thereof.

2. Related Art

A switching mode power supply apparatus rectifies AC power received froman external power source to obtain DC power, converts the DC power intoAC power by performing a switching operation, changes a voltage of theAC power using a transformer, and rectifies and smoothes the transformedAC power, thereby outputting smoothed DC power. The foregoing process iswidely used because it decreases power loss and heat generation comparedto a linear power supply apparatus that converts AC power into DC powerusing a passive element, such as a voltage-dividing resistor.

Referring to FIG. 1A, a switching mode power supply apparatus 1according to the related art includes a conversion unit 2 that convertsinput power into output power having a predetermined voltage byperforming a switching operation. An output unit 3 outputs the outputpower to an external device (not shown). A light emitting unit 4 emitslight if the voltage of the output power exceeds a predeterminedthreshold voltage. A light receiving unit 5 receives light from thelight emitting unit 4 and outputs a signal indicative of the voltage ofthe output power. A switching controller 6 controls the switchingoperation of the conversion unit 2 according to the voltage of theoutput power indicated by the signal output from the light receivingunit 5.

FIG. 1B is a detailed circuit diagram of a portion of the switching modepower supply apparatus 1 of FIG. 1A according to the related art.External AC power (e.g., an AC voltage of 220 V) is applied to a drainterminal of a metal-oxide semiconductor field effect transistor(MOSFET), a pulse-width modulated signal is generated based on thevoltage of the output power indicated by the signal output from thelight receiving unit 5 that is applied to a feedback (FB) terminal ofthe switching controller 6, and the pulse-width modulated signal isoutput from an output (OUT) terminal of the switching controller 6 andapplied to a gate terminal of the MOSFET.

However, if an excessive voltage is applied to the light receiving unit5 in an abnormal situation (e.g., when a short circuit occurs betweenthe drain terminal of the MOSFET and the FB terminal of the switchingcontroller 6), insulation between the light emitting unit 4 and thelight receiving unit 5 may be destroyed. Such an abnormal situation ismore likely to occur when the MOSFET and the switching controller 6 areintegrated in a single device. If the insulation is destroyed, a voltageapplied to the light emitting unit 4 will be transmitted to the lightreceiving unit 5, which may injure a user.

SUMMARY OF THE INVENTION

Accordingly, an aspect of the invention is to provide a switching modepower supply apparatus that prevents an excessive voltage from beingapplied to a light receiving unit in an abnormal situation to preventinjury to a user, and a power supply method thereof.

According to an aspect of the invention, a switching mode power supplyapparatus includes a conversion unit to convert input power into outputpower having a predetermined voltage; a light emitting unit to emitlight if the voltage of the output power exceeds a predeterminedthreshold voltage; a light receiving unit to receive the light emittedfrom the light emitting unit and output a signal indicative of thevoltage of the output power; a switching controller to control theswitching operation of the conversion unit according to the voltage ofthe output power indicated by the signal output from the light receivingunit; and a disconnection unit to disconnect power applied to the lightreceiving unit if the voltage of the power applied to the lightreceiving unit exceeds a predetermined trigger value.

According to an aspect of the invention, the disconnection unit mayinclude a Zener diode through which a current flows if the voltage ofthe power applied to the light receiving unit exceeds the predeterminedthreshold value; and a fusible element that is opened by the currentflowing through the Zener diode.

According to an aspect of the invention, the disconnection unit mayfurther include a switching unit that turns on if the voltage of thepower applied to the light receiving unit exceeds the predeterminedtrigger voltage to increase a current flowing through the fusibleelement.

According to an aspect of the invention, the fusible element maycomprise a fuse or a fusible resistor.

According to an aspect of the invention, a power supply method of aswitching mode power supply apparatus includes converting input powerinto output power having a predetermined voltage by performing aswitching operation; emitting light from a light emitting unit if thevoltage of the output power exceeds a predetermined threshold voltage;receiving the light emitted from the light emitting unit with a lightreceiving unit that outputs a signal indicative of the voltage of theoutput power; determining whether a voltage of power applied to thelight receiving unit exceeds a predetermined trigger voltage; anddisconnecting the power applied to the light receiving unit if thevoltage of the power applied to the light receiving unit exceeds thepredetermined trigger voltage.

According to an aspect of the invention, the disconnecting of the powermay include disconnecting the power using a Zener diode through which acurrent flows if the voltage of the power applied to the light emittingunit exceeds the predetermined trigger voltage; and a fusible elementthat is opened by the current flowing through the Zener diode.

According to an aspect of the invention, the disconnecting of the powermay further include using a switching unit that turns on if the voltageof the power applied to the light receiving unit exceeds thepredetermined trigger voltage to increase a current flowing through thefusible element.

According to an aspect of the invention, the fusible element may includea fuse or a fusible resistor.

According to an aspect of the invention, a disconnection unit isprovided for a switching mode power supply apparatus that includes aswitching controller to control a voltage of an output power of theswitching mode power supply apparatus by controlling a switchingoperation of the switching mode power supply apparatus according to asignal indicative of the voltage of the output power that is input to afeedback terminal of the switching controller; and a light receivingunit to output the signal indicative of the voltage of the output powerthat is input to the feedback terminal, the disconnection unitconnecting the light receiving unit to the feedback terminal to enablethe signal indicative of the voltage of the output power to be input tothe feedback terminal during a normal operation of the switching modepower supply apparatus, and disconnecting the light receiving unit fromthe feedback terminal if a voltage applied to the light receiving unitby the feedback terminal exceeds a predetermined trigger voltage.

Additional aspects and/or advantages of the invention will be set forthin part in the description that follows and, in part, will be obviousfrom the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects and advantages of the invention willbecome apparent and more readily appreciated from the followingdescription of embodiments of the invention, taken in conjunction withthe accompanying drawings of which:

FIG. 1A is a block diagram of a switching mode power supply apparatusaccording to the related art;

FIG. 1B is a detailed circuit diagram of a portion of the switching modepower supply apparatus of FIG. 1A according to the related art;

FIG. 2 is a block diagram of a switching mode power supply apparatusaccording to an aspect of the invention;

FIG. 3A is a detailed circuit diagram of a portion of the switching modepower supply apparatus of FIG. 2 according to an aspect of theinvention;

FIG. 3B is a detailed circuit diagram of a portion of the switching modepower supply apparatus of FIG. 2 according to an aspect of theinvention; and

FIG. 4 is a flow chart of a power supply method of a switching modepower supply apparatus according to an aspect of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to embodiments of the invention,examples of which are illustrated in the accompanying drawings, whereinlike reference numerals refer to like elements throughout. Theembodiments are described below in order to explain the invention byreferring to the figures.

Referring to FIG. 2, a switching mode power supply apparatus 100according to an aspect of the invention includes a conversion unit 10,an output unit 20, a light emitting unit 30, a light receiving unit 40,a switching controller 50, and a disconnection unit 60. The conversionunit 10 transforms input power into output power having a predeterminedvoltage, and includes a transformer (not shown) having a primary coiland a secondary coil. The input power, which is AC power received froman external power source (not shown), is rectified by a rectifier unit(not shown), the rectified power is converted to AC power by a switchingunit (not shown) under control of the switching controller 50, and theconverted AC power is applied across the primary coil of the transformerof the conversion unit 10.

AC power is induced in the secondary coil of the transformer of theconversion unit 10 according to a turns ratio of the primary coil andthe secondary coil, and the induced AC power is converted into DC outputpower via a diode (not shown) and a smoothing capacitor (not shown).However, it is understood that the conversion unit 10 may haveconfigurations other than that described above. For example, thetransformer may be omitted. Many such configurations are known in theart, and therefore will not be described here. Also, although theconversion unit 10 has been described above as converting AC input powerinto DC output power, the conversion unit 10 may also convert AC inputpower into AC output power, or DC input power into AC output power, orDC input power into DC output power.

The output unit 20 outputs the DC output power from the conversion unit10 to an external device (not shown).

The light emitting unit 30 emits light if a voltage of the output powerapplied to the output unit 20 exceeds a predetermined threshold voltage.The light receiving unit 40 receives the light from the light emittingunit 30, and outputs a signal indicative of the voltage of the outputpower to the switching controller 50. While not required in all aspects,the light emitting unit 30 and the light receiving unit 40 may beintegrated in a single chip in which they are insulated from each otherto electrically isolate the circuit to which the light emitting unit 30is connected from the circuit to which the light receiving unit 40 isconnected. Such a chip is known, for example, as a photocoupler, anoptocoupler, or an opto-isolator.

The switching controller 50 controls a switching operation of theswitching unit (not shown) of the conversion unit 10 according to thevoltage of the output power indicated by the signal output from thelight receiving unit 40 by applying a pulse-width modulated signal tothe switching unit (not shown) of the conversion unit 10 to adjust thevoltage of the output power output from the conversion unit 10. The ACinput power is input not only to the conversion unit 10, but is alsoinput to a VCC terminal of the switching controller 50 through asmoothing capacitor and a start-up resistor (see FIGS. 3A and 3B) toenable the switching controller 50 to operate during a start-upoperation. A Zener diode (see FIGS. 3A and 3B) connected between the VCCterminal and a CS terminal of the switching controller 50 limits avoltage applied to the VCC terminal to a Zener voltage of the Zenerdiode.

The disconnection unit 60 disconnects the light receiving unit 40 fromthe switching controller 50 if a voltage applied to the light receivingunit 40 exceeds a predetermined trigger voltage. The operation of thedisconnection unit 60 according to aspects of the invention will beexplained in detail with reference to FIGS. 3A and 3B.

Referring to FIG. 3A, a disconnection unit 60 of a switching mode powersupply apparatus 100 according to an aspect of the invention includes afusible resistor 60 b connected between a feedback (FB) terminal of theswitching controller 50 and the light receiving unit 40, and a Zenerdiode 60 a connected between ground and the junction between the fusibleresistor 60 b and the light receiving unit 40. However, it is understoodthat a fuse or any other fusible element may be used instead of thefusible resistor 60 b.

If an abnormal situation occurs (e.g., when a short circuit occursbetween a drain terminal of a MOSFET and the feedback (FB) terminal ofthe switching controller 50), a voltage applied to the feedback (FB)terminal exceeds the Zener voltage of the Zener diode 60 a, causing acurrent to flow from the feedback (FB) terminal to ground through thefusible resistor 60 b and the Zener diode 60 a. This current exceeds arated current of the fusible resistor 60 b, causing the fusible resistor60 b to open and disconnect the light receiving unit 40 from thefeedback (FB) terminal of the switching controller 50. Accordingly, anexcessive voltage is prevented from being applied to the light receivingunit 40 from the feedback (FB) terminal of the switching controller 50,thereby preventing insulation between the light emitting unit 30 and thelight receiving unit 40 from being destroyed. Here, a predeterminedtrigger voltage of the disconnection unit 60 is the Zener voltage of theZener diode 60 a. However, it is understood that any other voltagebreakdown element that conducts current when a voltage across it exceedsa predetermined trigger voltage may be used in place of the Zener diode60 a.

Alternatively, referring to FIG. 3B, a disconnection unit 60 of aswitching mode power supply apparatus 100 according to another aspect ofthe invention may further include a switching unit 60 c, such as atransistor, connected between ground and the junction between thefusible element 60 b and the light receiving unit 40, and a resistor 60d connected between ground and the Zener diode 60 a. A control terminalof the switching unit 60 c, such as a gate electrode of a transistor, isconnected to the junction between the Zener diode 60 a and the resistor60 d. However, it is understood that any other switching unit having acontrol terminal may be used instead of the transistor shown in FIG. 3B.Also, it is understood that additional circuit components, such asresistors and capacitors, may be included in the disconnection unit 60to control the operation of the switching unit 60 c.

If an abnormal situation occurs, e.g., when a short circuit occursbetween the drain terminal of the MOSFET and the feedback (FB) terminalof the switching controller 50, a voltage applied to the feedback (FB)terminal exceeds the Zener voltage of the Zener diode 60 a, causing acurrent to flow from the feedback (FB) terminal to ground through thefusible resistor 60 b, the Zener diode 60 a, and the resistor 60 d. Thecurrent flowing through the resistor 60 d creates a voltage drop acrossthe resistor 60 d, which increases a voltage applied to the controlterminal of the switching unit 60 c above a turn-on voltage of theswitching unit 60 c, which turns on the switching unit 60 c, whichconnects one end of the fusible resistor 60 b substantially to ground,thereby increasing a current flowing through the fusible resistor 60 babove the rated current of the fusible resistor 60 b, thereby causingthe fusible resistor 60 b to open more quickly than in the aspect of theinvention shown in FIG. 3A. Accordingly, insulation between the lightemitting unit 30 and the light receiving unit 40 is prevented from beingdestroyed, thereby preventing an accident in an abnormal situation.Here, like in the aspect of the invention shown in FIG. 3A, apredetermined trigger voltage of the disconnection unit 60 is the Zenervoltage of the Zener diode 60 a.

If an abnormal situation occurs in the switching mode power supplyapparatus 1 according to the related art, insulation between the lightemitting unit 4 and the light receiving unit 5 may be destroyed when avoltage of 500 V is applied to the light receiving unit 5. However, inthe switching mode power supply apparatus 100 according to aspects ofthe invention, tests have shown that insulation between the lightemitting unit 30 and the light receiving unit 40 will not be destroyedwhen a voltage of 3000 V or more is applied to the light emitting unit40.

A power supply method of the switching mode power supply apparatus 100according to an aspect of the invention will now be described withreference to FIG. 4.

First, input power is converted into output power having a predeterminedvoltage (S10). If the voltage of the converted output power at S10exceeds a predetermined threshold voltage, the light emitting unit 30emits light (S20).

Then, the light receiving unit 40 receives the light emitted at S20 andoutputs a signal indicative of the voltage of the output power (S30).

If the voltage of power applied to the light receiving unit 40 is over apredetermined trigger voltage (S40), the power applied to the lightreceiving unit 40 is disconnected (S50). Otherwise, the operation S40 isrepeated.

In the operation S50, if the voltage of the power applied to the lightreceiving unit 40 is over the predetermined trigger voltage in theoperation S40, the power applied to the light receiving unit 40 may bedisconnected using the flowing Zener diode 60 a and the fusible resistor60 b that is opened by the current flowing through the Zener diode 60 a,and possibly using the switching unit 60 c and the resistor 60 d toincrease the current flowing through the fusible resistor 60 b to openit more quickly.

As described above, a switching mode power supply apparatus and a powersupply method thereof according to aspects of the invention preventinjury to a user caused by damage to the switching mode power supplyapparatus caused by an abnormal situation in which an excessive voltageis applied to a light receiving unit.

Although several embodiments of the invention have been shown anddescribed, it would be appreciated by those skilled in the art thatchanges may be made in these embodiments without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

1. A switching mode power supply apparatus, comprising: a conversionunit to convert input power into output power having a predeterminedvoltage by performing a switching operation; a light emitting unit toemit light if the voltage of the output power exceeds a predeterminedthreshold voltage; a light receiving unit to receive the light emittedfrom the light emitting unit and output a signal indicative of thevoltage of the output power; a switching controller to control theswitching operation of the conversion unit according to the voltage ofthe output power indicated by the signal output from the light receivingunit; and a disconnection unit to disconnect power applied to the lightreceiving unit if a voltage of the power applied to the light receivingunit exceeds a predetermined trigger voltage, wherein the disconnectionunit detects a voltage of power applied to a feedback terminal of theswitching controller and prevents applying excessive voltage to thelight receiving unit from the feedback terminal.
 2. The switching modepower supply apparatus of claim 1, wherein the disconnection unitcomprises: a Zener diode through which a current flows if the voltage ofthe power applied to the light receiving unit exceeds the predeterminedtrigger voltage; and a fusible element that is opened by the currentflowing through the Zener diode.
 3. The switching mode power supplyapparatus of claim 2, wherein the fusible element comprises a fuse or afusible resistor.
 4. The switching mode power supply apparatus of claim2, wherein the predetermined trigger voltage is a Zener voltage of theZener diode.
 5. The switching mode power supply apparatus of claim 2,wherein the disconnection unit further comprises a switching unit thatturns on if the voltage of the power applied to the light receiving unitexceeds the predetermined trigger voltage to increase a current flowingthrough the fusible element.
 6. The switching mode power supplyapparatus of claim 5, wherein the fusible element comprises a fuse or afusible resistor.